13.56 MHz rectifier based on a microcrystalline silicon Schottky diodes for RFID application

Nowadays there is a lot of interest for the development of smart and low cost radio frequency identification (RFID) tags to replace barcodes. To achieve this goal of the reduction of production cost the components of RFID tag should be built on flexible substrates. These substrates require the use of materials deposited at low temperature. Our microcrystalline silicon with his deposition temperature (T<165°C) and his structural and electrical performance [1 2] is appropriate to the manufacturing of components dedicated to radio-frequency identification application. In the RFID circuitry one of the main components that should operate at 13.56 MHz is the rectifying device. One way to achieve the high frequency rectification is to fabricate Schottky diode devices [3] We fabricated on corning glass substrate Schottky diodes based on an interface between gold metal and microcrystalline silicon films deposited at low temperature (T<165°C) (Fig.l). The process starts by an isopropanol, acetone and de-ionized water cleaning of the glass substrate to delete any surface impurities. After that three films are deposited, aluminium for cathode contact, Highly N-doped microcrystalline silicon and silicon nitride for to reduce electric field stress at edge terminations and to minimize leakage current of diodes. Then by doing a first photolithographic step silicon nitride is etched to define ohmic bottom contact. Lightly N-doped microcrystalline silicon and gold metal are deposited immediately to form a Shottky contact. Finally a second photolithographic step was done to define the gold contact and to access aluminium bottom contact. Microcrystalline silicon and silicon nitride layers are deposited by using a classical capacitive 13.56 MHz PECVD reactor. Current — voltage measurement were performed at room temperature. Figure 2 shows the I-V characteristics of Au/μc-Si/Al Schottky diodes. For a voltage of −2V and +2V, current is 1.22 μA and 322 μA respectively. The rectifying factor is 264 and he indicates a good rectifying behaviour. The microcrystalline silicon Schottky diodes were then characterized in a rectifier circuit. For an incoming a.c. signal this Schottky diode allowed recovery of rectified voltage at 13.56 MHz. In conclusion Schottky diode based on microcrystalline silicon deposited at T<165 °C was fabricated and will be integrate RFID application on flexible substrates.